I am a civil engineer and worked with dams for a bit (though I am by no means an expert). For what it’s worth, earthwork dams are always a bit leaky. You’ve got an enormous pressure difference on one side of the dam versus the other, and that pushes water through underneath the dam. That being said, that IS a design consideration. So I wouldn’t worry.

High profile dams like that usually have a lot of eyes on them, but if you’re worried I would find out which state department is responsible for handling dams (in Indiana, the department of natural resources handles dams for example) and shoot them a FOIA request! They should have some construction records and inspection records. In the past couple of years the dam community on the whole has opted to be more transparent about dams in general so I don’t expect the report to be useless.

There’s a chance that your dam is an army core one and then I wouldn’t worry about it. The army core does a pretty good job with their dam and levies.